Measurements in quantum optics

Paolo Tombesi, Daniel F. Walls

Daniel Ish, Chase T. Ellis

Inspired by results in quantum information, we report the development of a formalism for optical sensing which abstracts the details of specific optical systems and allows us to form general bounds on measurement based only on the quantity to be measured. We find a universal bound that controls the performance of any passive optical system regardless of the technology used to construct it and that this bound is attained by a unique measurement scheme for each quantity of interest. Shockingly, our optical formalism is nearly identical to the quantum formalism, with essentially the same notions of the state to be measured and the operation of the measurement, along with an accompanying uncertainty principle.

Taichi Yamashima, Takahiro Kashiwazaki, Takumi Suzuki +8 more

Utilizing feedforward to perform adaptive quantum operations on one entangled state according to the measurement result of the other state enables measurement-based quantum information processing (QIP). Until now, the bandwidth of feedforward in optical QIP has been limited to around 100 MHz by measurement with electronics. A potential alternative is the utilization of an optical parametric amplifier (OPA). This optical device eliminates the need for electronic measuring devices and enables all-optical broadband feedforward. In this paper, we demonstrate a variable squeezing gate with an operation bandwidth of 1.3 THz by all-optical measurement-device-free feedforward. We utilize a periodically poled lithium niobate waveguide as a broadband OPA and perform continuous phase locking in our optical system. Experimental results demonstrate that our all-optical QIP operates at a THz clock frequency, representing a major step toward the realization of an ultra-fast quantum computer.

Stig Stenholm

Ritwik Dhara, Shyamal Guchhait, Meghna Sarkar +3 more

Quantum weak measurements became extremely popular in classical optics to amplify small optical signals for fundamental interests and potential applications. Later, as a more general extension, joint weak measurement has been proposed to extract the weak value from a joint quantum measurement. However, unlike traditional weak measurements, the detection of a joint weak value in the realm of classical optics remains less explored. Here, using the polarization-dependent longitudinal and transverse optical beam shift as a platform, we experimentally realize a classical optical analog of the quantum joint weak measurement. Polarization states are cleverly pre- and postselected, and different single and joint canonical position-momentum observables of the beam are experimentally extracted and subsequently analyzed for successful detection of the complex joint weak value. We envision that this work will find usefulness for gaining fundamental insights on quantum measurements and to tackle analogous problems in optics.

A. A. Vishenskii, I. A. Deriugin, Vitaliy N. Kurashov